The present invention relates to a full color organic device and more particularly to a structure of an organic device and a method for patterning the same.
The use of organic light emitting diode (OLED) displays is becoming increasingly common these days. The OLED displays can be used for various applications of various resolutions and sizes, including but not limited to, a mobile phone display, a tablet display, a laptop display and a television display.
The most common embodiment of full color OLED displays has a periodic arrangement of red, green, blue (RGB) or red, green, blue and white (RGBW) color emitting pixels. The number of such color emitting pixels in a display, the size of each of the individual pixels and the spacing between the pixels determine the OLED display characteristics for the intended application. The most common method of preparing commercial OLED displays is by vacuum sublimation of organic molecules from an organic source on to a partially finished display substrate. The organic materials forming the emission layer are formed at each of the target pixel locations on the display substrate, for either of the RGB or RGBW configurations by an appropriate patterning strategy. The emission layer is one of the constituting layers of the OLED device structure of each type of color pixel. There are two vacuum compatible patterning methods commonly employed in commercial OLED display manufacturing. In the case of RGB OLED displays, a physical shadow mask, commonly known as the fine metal mask (FMM), is employed for color pixel patterning. The FMM contains apertures matching the intended color pixel patterns of the OLED displays. The FMM, which is located in the path of the subliming emission layer materials, is at first aligned in close proximity with the display substrate in a vacuum environment before exposure to the path of the subliming organic materials. The FMM apertures are designed to match the pixel patterns covering the entire display substrate area so that all the color pixel layers can be deposited simultaneously. This FMM patterning method is repeated for each of the RGB colors on each of the display substrate to result in the creation of patterns of RGB emission layers on the display substrate. The FMM method, while successful thus far in mobile displays applications, may not be able to meet the increasing demand of higher resolutions in either the smaller mobile displays or the larger television displays, due to complications of mask preparation, mask alignment and accuracy of color reproduction. In the case of RGBW OLED displays, the FMM patterning method is not used. Instead, the color patterning step is performed by using color filter elements which are integrated with the display substrate prior to the formation of OLED devices on said substrate. A vacuum-deposited white OLED device structure with a broad emission spectrum is uniformly formed behind the color filter elements and which are designed to result in the RGB primary colors. As noted above, while the color filter elements for R, G and B pixels are incorporated in the display substrate, the fourth white or W pixel is also added to the display substrate design. The W pixel is unfiltered and can allow the entire white OLED emission spectrum to come through. The RGBW patterning method eliminates the complexities of the FMM patterning process in a vacuum environment and allows for the scaling of full color OLED displays to larger television displays using conventional design rules employed in the display substrate industry.
However, the use of color filter elements in the display substrate increases the number of processing steps required in its manufacturing process and therefore results in increased manufacturing costs. The RGBW patterning method is equally applicable for smaller mobile displays but the requirement of a fourth W pixel will reduce the display resolution, hence an unsatisfactory solution for most of these applications. In summary, both the RGB and RGBW OLED displays and their patterning methods have disadvantages in covering the whole range of display applications from smartphones to televisions and result in additional manufacturing costs due to the use of complex processes and increased number of processing steps.
U.S. Pat. No. 5,851,709 (Grande et al.), U.S. Pat. No. 5,688,551 (Littman et al.), U.S. Pat. No. 6,114,088 (Wolk et al.), U.S. Pat. No. 6,140,009 (Wolk et al.), U.S. Pat. No. 6,214,520 (Wolk e al.), U.S. Pat. No. 6,221,553 (Wolk et al.) teach the use of alternate OLED patterning techniques that do not employ either the FMM or the RGBW patterning methods. These alternate patterning techniques use the method of selective transfer of organic materials, which are uniformly deposited on a source substrate, to the display substrate. The selective transfer is accomplished by incorporating a patterned light-to-heat conversion (LHC) layer on the source substrate under the organic materials and by subsequently heating these LHC layers selectively with a source of intense radiation. This results in the selective transfer of the organic materials, either a single material layer or a multicomponent material layer, from the heated LHC regions. These prior art references cited above suffer from one or more of the following limitations. The method cited in U.S. Pat. No. 5,851,709, for instance, may teach the incorporation of a source substrate with physical apertures that mirror the targeted display substrate color pixel pattern, in combination with the patterned LHC layers, which are also incorporated on the same source substrate. The source substrate cited in this reference can be from the group of silicon, glass or ceramic substrates. Incorporating precise apertures on any of these substrates is an expensive process, involve complex fabrication processes and have size limitations thereby making this patterning method inherently more complex than the FMM method described in an earlier section. Finally, the resulting emission layer of the OLED color pixel on the display substrate is formed directly from the selective transfers from corresponding LHC regions of the source substrate. The method cited in U.S. Pat. No. 5,688,551, for instance, may teach the use of an integrated source substrate containing a donor sheet with pre-patterned LHC layers and uniformly covered with a layer of the organic emission layer materials. The integrated source substrate is aligned, in close proximity, with the display substrate. After alignment, the source substrate is subjected to an intense source of radiation, which results in the selective sublimation of emission layers from the LHC regions of the source substrate to the targeted pixel locations on the display substrate. The introduction of donor sheets for each color inside a vacuum environment adds complexities to the OLED display manufacturing process. Once again, the resulting emission layer of the OLED color pixel on the display substrate is formed directly from corresponding LHC regions of the source substrate. The methods cited in U.S. Pat. Nos. 6,114,088, 6,140,009, 6,214,520, 6,221,553 may teach a variety of options to use an integrated source substrate containing uniform LHC layers inserted between the substrate and a multicomponent organic layer unit. The said multicomponent unit has at least two active OLED device layers. The selective transfer of the entire multicomponent unit is accomplished by exposing the source substrate to an intense radiation according to a pattern, the said exposure pattern corresponding to the color pixel target locations on a display substrate. Once again, the resulting one or more active layers of the OLED device at the color pixel location on the display substrate are formed directly from the selective transfers from corresponding LHC regions of the integrated source substrate. This method additionally introduces more complexity in the manufacturing process since it requires the integration of a radiation source, such as a laser, which can write at the resolution of display pixel sizes. In summary, the search for alternate patterning methods to make RGB or RGBW OLED displays has been extensive over the years and many approaches based on selective transfers from LHC regions have been evaluated but with no clear success. The common theme in all the above methods is the direct transfers of functional organic layers from an LHC region of a source substrate to the corresponding regions on the display substrate. In all cases, the physical patterning process seems to be easy to demonstrate but the optoelectronic properties of the resulting OLED devices resulting from the direct transfer process have been inferior compared to their FMM or RGBW counterparts.
Therefore, there continues to be a need of a simple, cost effective and precise method and apparatus for patterning an organic device. The method and apparatus should allow high-resolution patterning of large and small displays. The method and apparatus should be versatile and capable of patterning displays of various sizes in desired resolutions, with precision. The method and apparatus should provide a high throughput and should be modular in operation.